Inorganic photocatalysts
became an essential and powerful tool
for the remediation of polluted water. However, important limitations
of photocatalysts in their colloidal form, especially nanosized, remain.
For instance, their separation from water after use and recovery,
which can be particularly demanding, time- and energy-wise. Considering
such aspects, supported catalysts bear significant advantages. However,
efforts still have to be made to develop processes that allow the
permanent and efficient immobilization of inorganic photocatalysts
in sustainable conditions, in order to maintain the advantages of
supported catalysts over colloidal ones. Herein, we report the use
of an aqueous-phase plasma-aided grafting (APPAG) process to produce
functional and efficient hybrid photocatalysts. More specifically,
based on cold plasma discharge (CPD), ZnO/Bi2MoO6 heterojunctions were permanently immobilized on polymer supports
generated by 3D-printing, with fractal-inspired designs. Three different
approaches of the APPAG process have been successfully used for the
immobilization of the inorganic phase, that is core–shell-assisted
direct grafting, indirect grafting and in situ complexation-assisted
precipitation (ISCAP). Noticeably, the latter technique has never
been reported before to our knowledge. These three immobilization
routes rely on different strategies and yield to distinct morphological
specificities, but all allow using mild synthesis conditions and producing
stable, active, permanently immobilized coatings of photocatalysts.
Regarding the preparation of the organic supports, two sorts of additive
manufacturing (AM) technologies were employed, namely fused-deposition
modeling (FDM) and liquid crystal diode (LCD)-based SLA (stereolithography).
The use of fractal geometries combined with AM permits the production
of supports with relatively high surface areas, in a single processing
step. Overall, the three plasma-based immobilization methods revealed
to be efficient and the performance of the different hybrid photocatalysts
have later been assessed through the photodegradation of Rhodamine
B dye under simulated sunlight irradiation and visible light only,
with promising results.
The present article summarizes antimony mine distribution, antimony mine drainage generation and environmental impacts, and critically analyses the remediation approach with special emphasis on iron oxidizing bacteria and sulfate reducing bacteria. Most recent research focuses on readily available low-cost adsorbents, such as minerals, wastes, and biosorbents. It is found that iron oxides prepared by chemical methods present superior adsorption ability for Sb(III) and Sb(V). However, this process is more costly and iron oxide activity can be inhibited by plenty of sulfate in antimony mine drainage. In the presence of sulfate reducing bacteria, sulfate can be reduced to sulfide and form Sb(2)S(3) precipitates. However, dissolved oxygen and lack of nutrient source in antimony mine drainage inhibit sulfate reducing bacteria activity. Biogenetic iron oxide minerals from iron corrosion by iron-oxidizing bacteria may prove promising for antimony adsorption, while the micro-environment generated from iron corrosion by iron oxidizing bacteria may provide better growth conditions for symbiotic sulfate reducing bacteria. Finally, based on biogenetic iron oxide adsorption and sulfate reducing bacteria followed by precipitation, the paper suggests an alternative treatment for antimony mine drainage that deserves exploration.
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